The present invention relates to the recording, storage and reading of magnetic data, particularly rotatable magnetic recording media, such as thin film magnetic disks having smooth surfaces for data zone. The invention has particular applicability to high density magnetic recording media exhibiting low noise and having improved flying stability, glide performance and head-media interface reliability for providing zero glide hits.
Magnetic disks and disk drives are conventionally employed for storing data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducing heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Magnetic disks are usually housed in a magnetic disk unit in a stationary state with a magnetic head having a specific load elastically in contact with and pressed against the surface of the disk.
Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk. It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. This objective becomes particularly significant as the areal recording density increases. The areal density (Mbits/in2) is the recording density per unit area and is equal to the track density (TPI) in terms of tracks per inch times the linear density (BPI) in terms of bits per inch.
The increasing demands for higher areal recording density impose increasingly greater demands on flying the head lower because the output voltage of a disk drive (or the readback signal of a reader head in disk drive) is proportional to 1/exp(HMS), where HMS is the space between the head and the media. Therefore, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk to be positioned in closer proximity with an attendant increase in predictability and consistent behavior of the air bearing supporting the head.
Most of the current magnetic disks are normally driven by the contact start stop (CSS) method, while many advanced disk drives, especially for lap top computers, are using the load/unload ramp design mechanism.
In the load/unload ramp design, the head is parked off the disk when the disk drive is not in use. This is conventionally done by the use of a load and unload ramp, wherein a load and unload tang of a head suspension assembly slides along, thereby moving the head between a position on the disk and a position parked off the disk.
In the CSS method, the head begins to slide against a landing zone of the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk landing zone. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates. The magnetic head unit is arranged such that the head can be freely moved in both the circumferential and radial directions of the disk in this floating state allowing data to be recorded on and retrieved from the surface of the disk at a desired position.
Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head begins to slide against the surface of the disk again and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from a stop and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk and stopping.
A conventional recording medium is shown in FIG. 1. Even thought FIG. 1 shows sequential layers on one side of the non-magnetic substrate 10, it is conventional to sputter deposit sequential layers on both sides of the non-magnetic substrate.
Adverting to FIG. 1, a sub-seed layer 11 is deposited on substrate 10, e.g., a glass or glass-ceramic substrate. Subsequently, a seed layer 12 is deposited on the sub-seed layer 11. Then, an underlayer 13, is sputter deposited on the seed layer 12. An intermediate or flash layer 14 is then sputter deposited on underlayer 13. Magnetic layer 15 is then sputter deposited on the intermediate layer, e.g., CoCrPtTa. A protective covering overcoat 16 is then sputter deposited on the magnetic layer 15. A lubricant topcoat (not shown in FIG. 1 for illustrative convenience) is deposited on the protective covering overcoat 16.
A conventional apparatus for manufacturing magnetic recording media is schematically illustrated in FIG. 2. The disk substrates travel sequentially from the heater to a sub-seed layer deposition station and a sub-seed layer is formed on the disk substrates. Then, the disk substrates travel to a seed layer station for deposition of the seed layer, typically NiAl. Subsequent to the deposition of the sub-seed layer and the seed layer, the disk substrates are passed through the underlayer deposition station wherein the underlayer is deposited. The disk substrates are then passed through the flash layer deposition station wherein typically a Co-alloy layer is deposited. The disks are then passed to the magnetic layer deposition station and then to the protective carbon overcoat deposition station.
In recent years, considerable effort has been expended to achieve high areal recording density. Among the recognized significant factors affecting recording density are magnetic remanance (Mr), coercivity, coercivity squareness (S*), signal/noise ratio, and flying height, which is the distance at which a read/write head floats above the spinning disk. Prior approaches to achieve increased areal recording density for longitudinal recording involve the use of dual magnetic layers separated by a non-magnetic layer as in Teng et al., U.S. Pat. No. 5,462,796, and the use of a gradient magnetic layer interposed between two magnetic layers as in Lal et al., U.S. Pat. No. 5,432,012.
However, the goal of achieving a rigid disk magnetic recording medium having an areal recording density of about 100 Gb/in2 has remained elusive. In particular, the requirement to further reduce the flying height of the head imposed by increasingly higher recording density and capacity renders the disk drive particularly vulnerable to head crash due to accidental glide hits of the head and media. To avoid glide hits, a smooth surface of data zone is desired.
Conventional techniques for producing a smooth surface on the disk include polishing and tape burnishing (buffing). See, for example, Nakamura et al., U.S. Pat. No. 5,202,810 and Bornhorst et al., U.S. Pat. No. 4,430,782. Typically, the polishing is done using a slurry and buffing is done after sputtering. However, these conventional techniques are attendant with numerous disadvantages. For example, it is extremely difficult to provide a clean and smooth surface due to debris formed by mechanical abrasions.
There exists a need for a magnetic recording medium having an areal recording density in excess of 10 Gb/in2, such as in the 20 Gb/in2 range, preferably up to 400 Gb/in2, exhibiting high coercivity and coercivity squareness and a relatively low Mrt (magnetic remanancexc3x97thickness), which can be employed for hard disk drives using GMR (giant magneto resistance) heads. For a GMR media, there exists a need to reduce the fly height to below 1 microinch (25 nm) with zero glide hits.
Disk glide height test (glide hits, glide avalanche), head fly height, and recording performance (output voltage, half peak height PW50, signal-to-noise ratio SNR) are sensitive to the spacing between the head and media. Accordingly, there exists a need for a system capable of providing a smooth topography of the non-magnetic substrate of a magnetic disk, thereby providing zero glide hits to enhance the reliability, tribology and long term durability of the data storage device.
An object of the present invention is a magnetic recording medium comprising a non-magnetic substrate having a very smooth surface of data zone.
Another object of the invention is a method of preparing a smooth surface of a non-magnetic substrate to provide zero glide hits, enhanced head-media interface reliability, tribology and glide performance of the head.
Additional advantages and features of this invention will be set forth in part in the description that follows and in part will become apparent to those having ordinary skill in the art upon examination of the following description and from the knowledge gained by practicing the invention. The advantages of this invention may be realized and obtained and are particularly pointed out in the claims.
According to the present invention, the foregoing and other objects are achieved in part by a magnetic recording medium comprising: a non-magnetic substrate having wholly or partially a smooth surface; and a magnetic layer formed on the upper surface; wherein Rmax, i.e., the smooth surface has a maximum difference in height between the highest and lowest points on the surface relative to a mean plane, is less than 10 nm, preferably less than 5 nm.
Another aspect of the invention is a method of manufacturing a magnetic recording medium, which method comprises surface treatment of a surface of a non-magnetic substrate by exposing the surface to a polishing means for cutting asperity of the surface, e.g., a moving tape.
Another aspect of the invention is a method of manufacturing a magnetic recording medium, which method comprises surface treatment of a surface of a non-magnetic substrate by exposing the surface to photon ozone treatment.
Additional advantages of this invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiments of this invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out this invention. As will be realized, this invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from this invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.